Crash Force Calculator

Work out crash force instantly with clear inputs, formula shown and shareable results.

About Crash Force Calculator

Crash force is mass times deceleration, where deceleration is v squared over twice the crush distance. That is why crumple zones matter so much: extending the crush from 0.3 to 0.6 m halves the peak force on everything inside the car.

Formula

Crash force

a = v^2 / (2 x crush distance); F = m x a; KE = 0.5 m v^2

Worked example

With the default values below, Crash Force Calculator returns Average force on the vehicle of 233.09. Change any input above and every figure here is recalculated in your browser.

Inputs used

Vehicle mass: 1,450 kg
Impact speed: 50 km/h
Crush distance: 0.6 m
Occupant mass: 78 kg

Results

Average force on the vehicle: 233.09 kN
Deceleration: 16.39 g
Force on a restrained occupant: 12.54 kN
Kinetic energy dissipated: 139.85 kJ

Step by step

1Values used
2Crash force
3Average force on the vehicle= 233.09 kN
4Deceleration= 16.39 g
5Force on a restrained occupant= 12.54 kN
6Kinetic energy dissipated= 139.85 kJ

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why do crumple zones help?

They extend the distance over which the car stops, and force is inversely proportional to that distance. Doubling the crush halves the force.

What deceleration can a person survive?

Restrained occupants routinely survive 20-30 g with modern belts and airbags. Above about 50-60 g survival becomes unlikely.